Firefox pdf viewer support for e10s (Bug 942707).

See https://bugzilla.mozilla.org/show_bug.cgi?id=942707
Exception running bootstrap method shutdown on uriloader@pdf.js: TypeError: globalMM.sendSyncMessage is not a function (resource://gre/modules/addons/XPIProvider.jsm -> jar:file:///Users/bdahl/Library/Application%20Support/Firefox/Profiles/dx3hp1j0.e10s/extensions/uriloader@pdf.js.xpi!/bootstrap.js:182:4) JS Stack trace: shutdown@resource://gre/modules/addons/XPIProvider.jsm -> jar:file:///Users/bdahl/Library/Application%20Support/Firefox/Profiles/dx3hp1j0.e10s/extensions/uriloader@bootstrap.js:182:5 < XPI_callBootstrapMethod@XPIProvider.jsm:4304:9 < XPI_updateAddonDisabledState@XPIProvider.jsm:4418:1 < AddonWrapper_userDisabledSetter@XPIProvider.jsm:6741:9 < set_userDisabled@extensions.xml:1084:11 < oncommand@about:addons:1:1